A רב was once asked, “We pray ומעביר אשמותינו. How do we know whether the תפילה is effective and it’s not a ברכה לבטלה? Perhaps we’re not forgiven.” The רב replied: “This is similar to a child who sees his friend with a box of candies asks for one. When he is turned down, what does the child do? He says a ברכה בקול רם and his friend has no choice but to give him the candy so it shouldn’t be a ברכה לבטלה.”
06/10/2021